1. Field of the Invention
The present invention relates to well kill additives and methods of making such additives, to well kill treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid with such additives and/or fluids, to methods of operating a well with such additives and/or fluids, and to methods of killing a well using such additives and/or fluids. In another aspect, the present invention relates to well kill additives comprising polymer, crosslinking agent, and filter aid and methods of making such additives, to well kill treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid with such additives and/or fluids, to methods of operating a well with such additives and/or fluids, and to methods of killing a well using such additives and/or fluids. In even another aspect, the present invention relates to well kill additives comprising a dry mixture of polymer, crosslinking agent, and filter aid and methods of making such additives, to well kill treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid with such additives and/or fluids, to methods of operating a well with such additives and/or fluids, and to methods of killing a well using such additives and/or fluids. In still another aspect, the present invention relates to well kill additives comprising a polymer, crosslinking agent, and diatomaceous earth (“DE”) and methods of making such additives, to well kill treatment fluids made therefrom and methods of making such fluids, to methods of modifying a well fluid with such additives and/or fluids, to methods of operating a well with such additives and/or fluids, and to methods of killing a well using such additives and/or fluids.
2. Description of the Related Art
Kill fluids are commonly placed in a wellbore during oil field wellbore operations, including drilling, wellbore completions, and workovers, to kill the well, i.e., prevent the intrusion of formation fluids into the wellbore while the well is open. The kill fluid is often maintained in the wellbore for the entire duration of the operation.
Conventional kill fluids known in the art are typically aqueous liquids, which contain a weighting agent, such as inert inorganic solids in solution or suspension, to increase the density of the fluid. The weighted kill fluid applies a hydrostatic pressure against the formation fluid, which is greater than the pressure exerted by the formation fluid attempting to intrude into the wellbore. This overbalanced hydrostatic pressure prevents the intrusion of formation fluids into the wellbore during performance of the given oil field wellbore operation which is necessary from an operational standpoint to prevent interference from formation fluids and which is also necessary from a safety standpoint. Maintenance of a sufficient hydrostatic pressure in the wellbore reduces the potential of a well kick or blow out.
Thickeners are often included in weighted kill fluids known in the art for leakoff inhibition. See, for example, Hudson et al, SPE Paper No. 10652, which discloses a weighted brine containing a fluid loss control agent, or U.S. Pat. No. 4,391,925 to Mintz et al, which discloses a multi-phase kill fluid comprising a number of constituents including a hydrocarbon, a surfactant, a clay and an organic polymer. Advantageous kill fluids are those which prevent formation fluid intrusion into the wellbore while preventing appreciable wellbore fluid leakoff into the formation. Fluid leakoff can undesirably result in formation damage, i.e., permeability reduction, which is manifested in reduced hydrocarbon recovery from the formation or reduced injectivity into the formation.
Under downhole conditions where the wellbore is in direct communication with voids, it can be extremely difficult to prevent fluid leakoff. Conventional kill fluids generally do not exhibit sufficient flow resistance to prevent them from escaping the wellbore into the formation matrix via the high permeability voids. Such leakoff can ultimately result in loss of the hydrostatic pressure overbalance which enables formation fluids to intrude into the wellbore, negating the primary function of the kill treatment. Although it is possible to maintain the hydrostatic pressure overbalance in the face of severe fluid leakoff by replenishing the lost kill fluid, this practice can be cost prohibitive.
U.S. Pat. No. 4,995,461, issued Feb. 26, 1991 to Sydansk noted that the utility of kill fluids was limited, particularly in the presence of voids in direct communication with the wellbore, and further noted a need existed for a kill treatment having utility in hydrocarbon recovery operations over a broad range of operating conditions, and particularly having utility when kill fluids are ineffective. Sydansk even further noted a need existed for a kill treatment, which is effective when severe voids in direct communication with the wellbore are present. Sydansk still further noted that a kill treatment was needed which prevents or minimizes the intrusion of formation fluids into the wellbore and prevents or minimizes the significant leakoff of wellbore fluid from the wellbore in the presence of such voids.
In an effort to overcome deficiencies noted by him in the prior art, Sydansk proposed in both U.S. Pat. Nos. 4,947,935, and 4,995,461, the use of a water soluble carboxylate crosslinking polymer along with a chromic carboxylate complex crosslinking agent for well kill treatment. Sydansk further teaches that the performance requirements of conformance improvement treatment polymers are different from those of kill treatment polymers. Thus, while U.S. Pat. No. 5,377,760, issued Jan. 3, 1995 to Merrill discloses addition of fibers to an aqueous solution of partially hydrolyzed polyacrylamide polymer, with subsequent injection into the subterranean to improve conformance, Sydansk teaches that such would not necessarily work for kill treatment.
Additionally, Merrill's conformance treatment method of mixing the fibers with the polymer solution followed by injection, requires a multiplicity of storage and mixing tanks, and a metering system which must be operated during the operation of the well. Specifically, a first tank will store a water and polymer solution, a second tank will store a water and cross-linking solution, and a third tank will be used to mix fibers with polymer solution from the first tank to create a polymer/fiber slurry. This polymer/fiber slurry is then metered from the third tank and combined with crosslinking solution metered from the second tank to the well bore.
As an advance over the above prior art, U.S. Pat. No. 6,016,869, issued Jan. 25, 2000, to Boyce D. Burts, Jr. for “Well kill additive, well kill treatment fluid made therefrom, and method of killing a well.” discloses an additive including a “dry mixture” of water soluble crosslinkable polymer, a crosslinking agent, and a reinforcing material of fibers and/or comminuted plant materials. The method of forming a fluid includes contacting the additive with water or an aqueous solution, with a method of treating the formation further including the step of injecting the fluid into the formation.
While not believed to be related prior art because they relate to different types of well operations, for completeness, attention is directed to five other similar “dry mixture” patents by Boyce D. Burts, Jr., which were filed on the same day (Oct. 31, 1997) as the '869 Patent: U.S. Pat. No. 6,218,343, issued Apr. 17, 2001, for “Additive for, treatment fluid for, and method of plugging a tubing/casing annulus in a well bore,” U.S. Pat. No. 6,102,121, issued Aug. 15, 2000, for “Conformance improvement additive, conformance treatment fluid made therefrom, method of improving conformance in a subterranean formation,” U.S. Pat. No. 6,098,712, issued Aug. 8, 2000, for “Method of plugging a well,” U.S. Pat. No. 6,016,879, issued Jan. 25, 2000, for “Lost circulation additive, lost circulation treatment fluid made therefrom, and method of minimizing lost circulation in a subterranean formation,” and U.S. Pat. No. 6,016,871, issued Jan. 25, 2000, for “Hydraulic fracturing additive, hydraulic fracturing treatment fluid made therefrom, and method of hydraulically fracturing a subterranean formation.”
A number of patents discuss the use of diatomaceous earth (“DE”) in a well operation.
U.S. Pat. No. 3,380,542, issued Apr. 30, 1968 to Clear, for restoring lost circulation discloses a oil-based drilling fluid, containing a slurry of diatomite and asbestos, used to restore lost circulation during well drilling operations.
U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, discloses that various formation sealing agents have been used in the art to form formation seals and/or filter cakes on the wall of a well bore, including diatomaceous earth.
U.S. Pat. No. 4,110,225, issued Aug. 29, 1978 to Cagle, discloses that zones of lost circulation and other undesired fluid communication channels into a wellbore are sealed by isolating a volume in the well including such a zone and applying greater than formation pressure to a novel slurry spotted in the zone until it hardens into a solid, drillable seal. The slurry contains per barrel from 5-50 pounds diatomaceous mix, from about 35 to about 350 pounds of oil well cement, and at a minimum about 5 to 6 pounds of a flake type lost-circulation agent. This '225 patent cites a number of patents that disclose cement/diatomaceous earth compositions, including U.S. Pat. Nos. 2,585,336; 2,793,957; 2,961,044; 3,467,198; and 3,558,335.
Regarding these patents, the '225 patent notes the following:                Regarding U.S. Pat. No. 2,585,336, the '225 patent notes, “a mixture is made using from 2% to 100% diatomaceous earth, compared to the content of the cement in the slurry. The aim of the inventors was to prevent perlite from settling and to produce a lightweight cement. The diatomaceous earth-cement described in the disclosure is a mixture of Portland cement, perlite and diatomaceous earth, lime, and asbestos fibers.”        Regarding U.S. Pat. No. 2,793,957, the '225 patent notes, “refers to a highly permeable cement formed by use of the same basic mixtures of diatomaceous earth with Portland cement, the diatomaceous earth present being from five to seven times the proportion of the Portland cement in the slurry. The aim of the inventors was to produce a light highly permeable cement, entirely opposite to the purpose of my invention.”        Regarding U.S. Pat. No. 2,961,044, the '225 patent notes, “discusses and claims a cement composition which has diatomaceous earth in the amounts of from 30% to 70% of the Portland cement. The reason for using the diatomaceous earth was to prevent the strength retrogression of a salt-saturated cement. Thus, while Shell wishes (among other uses) to employ his mixture for squeeze cementing, he produces a relatively high-strength cement plug. There is a real tendency when redrilling such a plug for the bit to be deflected or sidetracked so that the new hole is beside rather than through the bore and the seal is ineffective. This is completely different from my invention which minimizes such tendency by producing a plug at least as drillable as the formation in which it is set. Also, Shell is directed to operations using salt-saturated cement slurries, while I prefer using a fresh or brackish water slurry. I employ lost-circulation agents; he makes no teaching of using such additives. Accordingly, his teaching is quite far from mine.”        Regarding both U.S. Pat. Nos. 3,467,198 and 3,558,335, the '225 patent notes, “describe cement compositions having diatomaceous mix present in the amounts from 0.5% to 10% of the amount of Portland cement present to prevent solids-settling.”        
U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, discloses slurries to seal permeable earth formations encountered in the drilling of wells, comprising finely divided paper, diatomaceous earth, and in a further embodiment, lime. A slug of the slurry is spotted at the locus of the permeable formation and defluidized to form a formation seal on which a mud sheath is then deposited.
U.S. Pat. No. 4,505,751, issued Mar. 19, 1985, discloses a silicate/silica cement in oil field applications, including diatomaceous earth as a species of silica compound.
While not believed to be analogous prior art because it relates to earthen pits (for example a ditch) and not to subterranean wellbores nor well operations, U.S. Pat. No. 5,947,644, issued Sep. 7, 1999 to Gibbons et al., is included herein for completeness because it discloses a gelable slurry of aqueous solvent, a crosslinkable polymer, a crosslinking agent, and unconsolidated solids such as diatomaceous earth. This gelable slurry is placed in an earthen pit and allowed to form into a fluid impermeable barrier wall in the earthen pit. The polymer serves to bind the unconsolidated solids to convert the gelable slurry to a nondeformable gelled continuum of consolidated solids, which forms the barrier wall in the earthen pit. As disclosed in the '644 Patent in the Summary of the Invention section, at col. 1, lines 57-67, this gelable slurry is prepared by first forming a liquid gelation solution of the polymer and crosslinking agent, to which is subsequently mixed with the unconsolidated solids, or alternatively, by sequentially mixing the aqueous solvent, crosslinkable polymer, and polymer crosslinking agent with the unconsolidated solids.
Thus, in spite of the advancements in the prior art, there still need for further innovation in well kill additives.
There is need for further innovation for well kill additives utilizing a water soluble polymer.
There is another need for a well kill additive which would allow for simplification of the mixing equipment.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.